The present invention relates to plasma processing apparatuses and, more particularly, to a microwave plasma processing apparatus and a plasma processing method for acting plasma generated by a microwave onto an object to be processed such as a wafer, etc.
In recent years, with densification and miniaturization of semiconductor products, plasma processing apparatuses have been used for a process such as film deposition, etching, ashing, etc. in a manufacturing process of a semiconductor product. Especially, a microwave plasma processing apparatus that generates plasma using a microwave is capable of stably generating plasma even in a high-vacuum state of a relatively low pressure such as 0.1-10 mToor. For this reason, a microwave plasma processing apparatus using 2.45 GHz microwave, for example, has attracted attention.
Generally, in a microwave plasma processing apparatus, a dielectric plate that can transmit a microwave is provided to a ceiling part of a process container which is made to be evacuatable, and a disc-like, flat antenna member (microwave radiation member) is attached to the dielectric plate. Many through holes (slots) are formed in the antenna member so as to introduce a microwave, which is supplied at the center thereof and propagates in radial directions, into the process container through the slots. Plasma of a process gas is generated by the microwave introduced into the process container, and plasma processing is applied to the semiconductor wafer placed in the process container.
Japanese Patent Publications No. 2722070 and No. 2928577 disclose a microwave plasma processing apparatus having an antenna member for introducing a microwave into a process container. The antenna member disclosed in these patent publications has a circular shape, and many slots or slot pairs are formed along a plurality of concentric circles. Also disclosed is an antenna member having many slots or slot pairs arranged spirally.
A microwave supplied to the central part of the circular antenna member propagates in a radial direction, and the direction is changed by the slots and is introduced into the process container after passing through the dielectric plate. Under such a condition, a surface wave propagating in radial directions (through the dielectric plate) between the antenna member and the plasma is reflected by an outer peripheral surface of the dielectric plate and returns to the central part. Here, in a case where the slots of the antenna member are arranged along a plurality of concentric circles, the surface wave reflected by the entire peripheral surface of the dielectric plate is concentrated into the central part of the antenna member. Therefore, the electric field of the surface wave is large at the central part of the antenna, and decreases toward the peripheral parts.
FIG. 1 is an illustration showing propagation of the surface wave in the antenna member having concentrically arranged slots and a distribution of an electron density in a plasma space. FIG. 1(a) shows surface wave propagation of the dielectric plate in correspondence to the antenna member, and FIG. 1(b) is a graph showing a distribution of electron density of a plasma density in a radial direction of the antenna member. As shown in FIG. 1(b), the electron density ne of the plasma space is maximum at the central part of the antenna member, and the electron density ne decreases toward the periphery of the antenna member. Therefore, in the antenna member having concentrically arranged slots, there is a problem in that the plasma density is uneven since the plasma density corresponding to the central part of the antenna member is higher than the plasma density in the periphery.
It is a general object of the present invention to provide an improved and useful microwave plasma processing apparatus and a plasma processing method in which the above-mentioned problems are eliminated.
A more specific object of the present invention is to provide a microwave plasma processing apparatus, a plasma processing method and an antenna member which can make a plasma density uniform in a radial direction of an antenna member.
In order to achieve the above-mentioned objects, there is provided according to one aspect of the present invention a microwave plasma processing apparatus which applies plasma processing to a substrate to be processed comprising: a process container provided therein with a placement stage on which the substrate to be processed is placed; a microwave generator which generates a microwave and supplies the microwave to the process container; and a microwave radiation member provided between the microwave generator and the process container so as to radiate the microwave to a space of the process container, wherein the microwave radiation member has a plurality of slots arranged along a plurality of circumferences, and the plurality of circumferences are non-concentric to each other.
In the above-mentioned invention, the centers of the plurality of circumferences may be eccentric in different directions to each other with respect to the center of the microwave radiation member. Additionally, the centers of the plurality of circumferences may be eccentric in the same direction to each other with respect to the center of the microwave radiation member, and an amount of eccentricity of the centers of the plurality of circumferences may increase toward a periphery of the microwave radiation member. Further, a slot pair may be formed by one of the slots and an adjacent one of the slots arranged in a T-shape, and a plurality of the slot pairs may be arranged along the plurality of circumferences.
Additionally, there is provided according to another aspect of the present invention a plasma processing method using a microwave plasma processing apparatus which applies plasma processing to a substrate to be processed, comprising; a process container provided therein with a placement stage on which the substrate to be processed is placed; a microwave generator which generates a microwave and supplies the microwave to the process container; and a microwave radiation member provided between the microwave generator and the process container so as to radiate the microwave to a space of the process container, wherein the microwave radiation member has a plurality of slots arranged along a plurality of circumferences, and the plurality of circumferences are non-Concentric to each other, the method comprising: placing the substrate to be processed on the placement stage so that a processing surface of the substrate faces the microwave radiation member; supplying the microwave to the microwave radiation member so as to introduce the microwave into the process container through the non-concentrically arranged slots; and generating plasma in the process container by the introduced microwave so as to apply a plasma process to the substrate by the generated plasma.
Additionally, there is provided according to another aspect of the present invention a microwave radiation member used for a microwave plasma processing apparatus comprising a process container which applies a plasma process and a microwave generator which generates a microwave and supplies to the process container, wherein the microwave radiation member is attached to the process container and is connected to the microwave generator, and the microwave radiation member has a plurality of slots arranged along a plurality of circumferences non-concentric to each other so as to introduce the microwave into the process container through the plurality of slots.
In the above-mentioned invention, the centers of the plurality of circumferences may be eccentric in different directions to each other with respect to the center of the microwave radiation member. Additionally, the centers of the plurality of circumferences may be eccentric in the same direction to each other with respect to the center of the microwave radiation member, and an amount of eccentricity of the centers of the plurality of circumferences may increase toward a periphery of the microwave radiation member. Further, a slot pair may be formed by one of the slots and an adjacent one of the slots arranged in a T-shape, and a plurality of the slot pairs may be arranged along the plurality of circumferences.
According to the above-mentioned invention, the density of plasma to generate can be uniformized by arranging the plurality of slots of the microwave radiation member along the plurality of non-concentric circumferences. By making the plurality of non-concentric circumferences eccentric in different directions, the electron density, which tends to increase at the central part of the microwave radiation member, can be decreased so as to uniformize the plasma density. Moreover, the plasma density can be uniformized by intentionally generating a variation in the distribution of electron density by making the plurality of non-concentric circumferences eccentric in the same direction and correcting by synthesizing with a variation of the plasma density due to other causes.
Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.